The coelacanths,(Source: Wikipedia)_constitute a now rare order of fish that includes two extant species in the genus Latimeria: the West Indian Ocean coelacanth (Latimeria chalumnae) and the Indonesian coelacanth (Latimeria menadoensis). They follow the oldest known living lineage of Sarcopterygii (lobe-finned fish and tetrapods), which means they are more closely related to lungfish, reptiles and mammals than to the common ray-finned fishes. They are found along the coastlines of the Indian Ocean and Indonesia.Since there are only two species of coelacanth and both are threatened, it is the most endangered order of animals in the world. The West Indian Ocean coelacanth is a critically endangered species.
Coelacanths belong to the subclass Actinistia, a group of lobed-finned fish related to lungfish and certain extinct Devonian fish such as osteolepiforms, porolepiforms, rhizodonts, and Panderichthys.Coelacanths were thought to have gone extinct in the Late Cretaceous,around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa.The coelacanth was long considered a “living fossil” because it was believed to be the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive,and to have evolved into roughly its current form approximately 400 million years ago.Several recent studies have shown that coelacanth body shapes are much more diverse than was previously thought, however.
Latimeria chalumnae and L. menadoensis are the only two known living coelacanth species.The word "coelacanth" is derived from the Greek for “hollow spine”, because of the fish's unique hollow spine fins.Coelacanths are large, plump, lobe-finned fish that grow up to 1.8 meters. They are nocturnal piscivorous drift-hunters.The body is covered in cosmoid scales that act as armor. Coelacanths have eight fins – 2 dorsal fins, 2 pectoral fins, 2 pelvic fins, 1 anal fin and 1 caudal fin. The tail is very nearly equally proportioned and is split by a terminal tuft of fin rays that make up its caudal lobe. The eyes of the coelacanth are very large, while the mouth is very small. The eye is acclimatized to seeing in poor light by rods that absorb mostly low wavelengths. Coelacanth vision has evolved to a mainly blue-shifted color capacity.
DNA_A group led by: Chris Amemiya and Neil Shubin published the genome sequence of the coelacanth in the journal Nature. The African coelacanth genome was sequenced and assembled using DNA from a Comoros Islands Latimeria chalumnae specimen. It was sequenced by Illumina sequencing technology and assembled using the short read genome assembler ALLPATHS-LG.
ECOLOGY_Anjouan Island and the Grande Comore provide ideal underwater cave habitats for coelacanths. The islands' underwater volcanic slopes, steeply eroded and covered in sand, house a system of caves and crevices which allow coelacanths resting places during the daylight hours. These islands support a large benthic fish population that help to sustain coelacanth populations.During the daytime, coelacanths will rest in caves anywhere from 100 to 500 meters deep; others migrate to deeper waters.The cooler waters (below 120 meters) reduce the coelacanths' metabolic costs. Drifting toward reefs and night feeding saves vital energy.Resting in caves during the day also saves energy otherwise used to fight currents.Coelacanths are nocturnal piscivores who feed mainly on benthic fish populations.Drifting along the lava cliffs, they presumably feed on whatever fish they encounter.
Coelacanths are fairly peaceful when encountering others of their kind; remaining calm even in a crowded cave. They do avoid body contact, however, withdrawing immediately if contact occurs. When approached by foreign potential predators (e.g. a submersible), they show panic flight reactions, suggesting that coelacanths are most likely prey to large deepwater predators. Shark bite marks have been seen on coelacanths; sharks are common in areas inhabited by coelacanths.Electrophoresis testing of 14 coelacanth enzymes shows little genetic diversity between coelacanth populations. Among the fish that have been caught were about equal numbers of males and females.Population estimates range from 210 individuals per population all the way to 500 per population.Because coelacanths have individual color markings, scientists think that they recognize other coelacanths via electric communication.
LIFE HISTORY_Coelacanths are ovoviviparous, meaning that the female retains the fertilized eggs within her body while the embryos develop during a gestation period of over a year. Typically, females are larger than the males; their scales and the skin folds around the cloaca differ. The male coelacanth has no distinct copulatory organs, just a cloaca, which has a urogenital papilla surrounded by erectile caruncles. It is hypothesized that the cloaca everts to serve as copulatory organ.Coelacanth eggs are large with only a thin layer of membrane to protect them. Embryos hatch within the female and eventually are given live birth. Young coelacanths resemble the adult, the main differences being an external yolk sac, larger eyes relative to body size and a more pronounced downward slope of the body. The juvenile coelacanth's broad yolk sac hangs below the pelvic fins. The scales and fins of the juvenile are completely matured; however, it does lack odontodes, which it gains during maturation.
CONSERVATION_Because little is known about the coelacanth, the conservation status is difficult to characterize. According to Fricke et al. (1995), there should be some stress put on the importance of conserving this species. From 1988 to 1994, Fricke counted some 60 individuals on each dive. In 1995 that number dropped to 40. Even though this could be a result of natural population fluctuation, it also could be a result of overfishing. Coelacanths usually are caught when local fishermen are fishing for oilfish. Fishermen sometimes snag a coelacanth instead of an oilfish because they traditionally fish at night, when oilfish (and coelacanths) feed. Before scientists became interested in coelacanths, they were thrown back into the water if caught. Now that there is an interest in them, fishermen trade them in to scientists or other officials once they have been caught. Before the 1980s, this was a problem for coelacanth populations. In the 1980s, international aid gave fiberglass boats to the local fishermen, which resulted in fishing out of coelacanth territories into more fish-productive waters. Since then, most of the motors on the boats have broken down so the local fishermen are now back in the coelacanth territory, putting the species at risk again. Different methods to minimize the number of coelacanths caught include moving fishers away from the shore, using different laxatives and malarial salves to reduce the quantity of oilfish needed, using coelacanth models to simulate live specimens, and increasing awareness of the need to protect the species. In 1987 the Coelacanth Conservation Council was established to help protect and encourage population growth of coelacanths.
In 2002, the South African Coelacanth Conservation and Genome Resource Programme was launched to help further the studies and conservation of the coelacanth. The South African Coelacanth Conservation and Genome Resource Programme focuses on biodiversity conservation, evolutionary biology, capacity building, and public understanding. The South African government committed to spending R10 million on the program.
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